Scaling of transepithelial potential difference in the mammalian trachea

Tracheal epithelia of different mammalian species differ widely with regard to the relative rates of Na⁺ absorption and Cl⁻ secretion. However, the short circuit current, a measure of total ion transport, appears to be consistently greater in large than in small mammals. Thus, we hypothesized that the in vivo tracheal electrical potential difference (PD) would vary among species as a function of body mass (M). To test this hypothesis we measured PD in ten mammalian species that ranged 1000-fold in mass. The results in mV (mean ± SE, lumen negative) were: 11.4 ± 1.0 in mice; 11.6 ± 1.2 in gerbils; 12.9 ± 1.4 in rats; 19.3 ± 0.9 in guinea pigs; 27.2 ± 2.2 in ferrets; 23.0 ± 1.6 in cats; 27.0 ± 0.6 in rabbits; 32.5 ± 2.6 in dogs; 37.0 ± 1.9 in sheep; and 49.0 ± 3.3 in pigs. Log-log correlation analysis of mean PD (in mV) and M (in kg) yielded PD = 20.9 M^0.19 (r = 0.96, P < 0.001). Analysis of published short circuit current (SCC, in μA/cm²) data revealed a similar relationship: SCC = 38.2 M^0.21. Thus, the transepithelial electrical potential and active charge transport by the tracheal epithelium are allometric variables that may have direct physiological significance. These results raise questions regarding the importance of net osmotic solute and water transport across the tracheal epithelium.     

Colonic and esophageal transepithelial potential difference in cystic fibrosis

To evaluate differences in the expression of cystic fibrosis (CF) transport defects in the gastrointestinal tract of subjects with CF, in vivo measurements of colonic and esophageal transepithelial electrical potential difference (PD) were performed before and during amiloride superfusion in CF and healthy subjects. Esophageal PD before (-16 +/- 2 vs. -16 +/- 3 mV) and after (-14 +/- 2 vs. -15 +/- 0.3 mV) superfusion with amiloride were similar for CF and healthy subjects. Basal rectosigmoid colon PD was also similar (CF: mean -23 +/- 6 and maximal -37 +/- 9 mV; normal: mean -26 +/- 5 and maximal -45 +/- 11 mV) in both groups. However, with amiloride superfusion (10(-4) M) the colonic PD in CF subjects was almost abolished (95% +/- 15% inhibition), whereas the PD in healthy subjects was only partially reduced (42% +/- 6%) (p less than 0.05). The greater inhibition with amiloride in CF, which was evident in absolute terms (26 +/- 4 vs. 16 +/- 3 mV for controls, p less than 0.05) as well as relative terms, could not be ascribed to a difference in mineralocorticoid secretion rates, because 24-h urine excretion of aldosterone and 17 hydroxy and 17 ketosteroids were similar in both groups. Freshly excised colonic epithelia from 1 CF and 3 non-CF subjects were studied in Ussing chambers, and a similar difference in amiloride responsiveness noted: PD and short-circuit current declined 33% +/- 2% and 37% +/- 4%, respectively, in seven tissues from the colons of 3 patients without CF, whereas both PD and short-circuit current were fully inhibited (100%) in all three tissues from the CF patient. As the presence of an amiloride-insensitive component of short-circuit current in non-CF colon is largely due to electrogenic Cl- secretion, the demonstration that this component was absent both in vivo and in vitro in CF colon establishes the presence of a defect in electrolyte transport in CF colon, a defect consistent with recent reports of absent electrogenic Cl- secretion in CF intestine.     

High altitude impairs nasal transepithelial sodium transport in HAPE-prone subjects.

High-altitude pulmonary oedema (HAPE) occurs in predisposed individuals at altitudes >2,500 m. Defective alveolar fluid clearance secondary to a constitutive impairment of the respiratory transepithelial sodium transport contributes to its pathogenesis. Hypoxia impairs the transepithelial sodium transport in alveolar epithelial type II cells in vitro. If this impairment is also present in vivo, high-altitude exposure could aggravate the constitutive defect in sodium transport in HAPE-prone subjects, and thereby further facilitate pulmonary oedema. Therefore, the aim of the current study was to measure the nasal potential difference (PD) in 21 HAPE-prone and 29 HAPE-resistant subjects at low altitude and 30 h after arrival at high altitude (4,559 m). High-altitude exposure significantly decreased the mean +/- SD nasal PD in HAPE-prone (18.0 +/- 6.2 versus 12.5 +/- 6.8 mV) but not in HAPE-resistant subjects (25.6 +/- 9.4 versus 22.9 +/- 9.2 mV). This altitude-induced decrease was not associated with an altered amiloride-sensitive fraction, but was associated with a significantly lower amiloride-insensitive fraction of the nasal PD. These findings provide evidence in vivo that an environmental factor may impair respiratory transepithelial sodium transport in humans. They are consistent with the concept that in high-altitude pulmonary oedema-susceptible subjects, the combination of a constitutive and an acquired defect in this transport mechanism facilitates the development of pulmonary oedema during high-altitude exposure.     

Acidic pH hyperpolarizes nasal potential difference

Nasal potential difference (NPD) has served as a non-invasive diagnostic method for cystic fibrosis (CF) a disease of chloride channel expression and function in secretory epithelia. Investigators have also used NPD to demonstrate ion transport abnormalities in newborns with respiratory distress. Standard perfusates for diagnostic NPD studies include the use of amiloride, replacement of chloride with gluconate, cAMP agonists, and nucleotides such as ATP. The pH of these perfusates may also be relevant to NPD studies as we have previously shown that the respiratory epithelia in mammals express CLC-2, which is a pH sensitive chloride channel. We hypothesized that acidic pH might activate chloride secretion in vivo if CLC-2 is present in human respiratory epithelia. Our objective was to determine the effect of acidic pH on NPD measurements and the frequency of expression of CLC-2 in normal subjects. Healthy adults were recruited and CLC-2 protein expression was detected in 20 of 29 primary nasal epithelial cell cultures. Acidic pH stimulated NPD responses in 33% of subjects. These findings suggest that pH sensitive alternative pathways are available for modulation in human respiratory epithelia and that NPD protocols should standardize pH of perfusates.     

Effect of luminal ions on the transepithelial electrical potential difference of human rectum

Skin electrodes are the most convenient reference electrodes for clinical measurements of electrical potential differences (pd) across the epithelium of the alimentary tract but the presence of an electrical charge on normal skin introduces an error. In the present study, by comparison with results obtained using subcutaneous and intravenous electrodes, it was shown that an intradermal injection of saline abolished the skin potential differences. This simple method, therefore, allows skin electrodes to be used to measure the true transepithelial potential differences of gut mucosa. The method was applied to investigate the effect on the rectal potential difference of altering the composition of the luminal solutions. Changes in the cations (sodium, potassium, magnesium) showed that sodium was the most important cationic determinant of the potential difference, especially when sodium absorption was stimulated by giving mineralocorticoids. Changes in the anions (chloride, iodide, bromide, nitrate, bicarbonate, sulphate, phosphate, citrate, and acetate) indicated that the molecular size of the anion rather than its chemical nature was the significant factor and suggested that the ions had to cross a barrier relatively impermeable to anions of radius greater than 3.5 to 4 A degrees . Changes in osmolality and glucose concentration were without effect.     

Measurement of nasal potential difference in mild asthmatics

STUDY OBJECTIVE: To determine whether ion transport or barrier function across the nasal epithelium are altered in asthmatics. DESIGN: In this pilot study, the nasal potential difference (PD) was measured using the technique established by Knowles and colleagues. A flowing agar bridge made electrical contact with the surface of the nasal epithelium along the floor of the nose. This bridge was referenced to a cutaneous electrode to determine the PD across the nasal epithelium. Changes in nasal PD in response to amiloride, chloride-free medium, and chloride-free medium containing isoproterenol were measured, and responses of asthmatics and healthy control subjects were compared. PARTICIPANTS: Measurements were made in eight adult nonasthmatic subjects and 6 adult asthmatic subjects. All asthmatics had mild intermittent asthma. MEASUREMENTS AND RESULTS: Continuous measurements of nasal PD were obtained while the nasal surface was perfused consecutively with saline solution (NaCl-containing solution), saline solution plus 100 micro mol/L amiloride, chloride-free solution plus amiloride, and chloride-free solution with amiloride plus 10 micro mol/L isoproterenol (a beta-adrenergic agonist). No significant differences in baseline PD or change in PD in response to changes in perfusate were found between the two groups. CONCLUSIONS: Our results suggest that ion transport and barrier function of patients with mild asthma are normal. Therefore, by contrast to cystic fibrosis, changes in salt and water transport across airway epithelium may not contribute to accumulation of mucous secretions in asthma.     

Effect of lidamidine on transepithelial potential difference evoked by prostaglandin E2 in human jejunum

The effect of the infusion of lidamidine, an antidiarrheal drug, on the change in transepithelial potential difference (TPD) induced by the infusion of prostaglandin E2 (PGE2) was examined in perfused human jejunum in vivo. The increase in luminal negativity of TPD produced by 3 X 10(-7) M PGE2 was significantly decreased from 2.8 +/- 0.5 mV to 1.2 +/- 0.5 mV by the superimposed infusion of 2 X 10(-3) M lidamidine. This result may suggest that lidamidine has an inhibitory effect on intestinal Cl secretion which is stimulated by PGE2.     

Reproducibility of nasal potential difference measurements in cystic fibrosis

BACKGROUND: Nasal potential difference (NPD) measurement has been advocated as a diagnostic tool for cystic fibrosis (CF) patients and as a method for assessing the response to new therapies. The purpose of this study was to examine the reproducibility of NPD measurements performed in a single center. METHODS: A total of 68 CF patients with a mean (+/- SD) age of 16 +/- 8 years (age range, 6 to 52 years) underwent NPD measurements on at least two occasions. RESULTS: A total of 25 patients with classic CF (mean age, 21 +/- 8 years) and 43 patients with nonclassic CF (mean age, 14 +/- 8 years) underwent sweat tests and NPD measurements. The mean sweat chloride values were 102 +/- 18 and 54 +/- 14 mEq/L, respectively, for classic CF and nonclassic CF groups. All patients underwent repeat NPD measurements. The basal NPD and the response to amiloride (DeltaAmil) and response to Cl(-) free and isoproterenol (DeltaCl(-) free + iso) were very similar in both measurements. In the classic CF group, the basal potential difference values were -40 +/- 12 vs -39 +/- 11 mV (p = 0.57), respectively, for the first and second measurements; 27 +/- 9 vs 26 +/- 10 mV (p = 0.55), respectively, for DeltaAmil; and 2.1 +/- 3.8 vs 0.4 +/- 2.9 mV (p = 0.07), respectively, for DeltaCl(-) free + iso. In the nonclassic CF group, the values were -32 +/- 13 vs -28 +/- 10 mV (p = 0.008), respectively; 19 +/- 10 vs 17 +/- 8 mV (p = 0.388), respectively; and -3.2 +/- 4.6 vs -3.3 +/- 4.4 mV (p = 0.876), respectively. CONCLUSION: When performed in a single center, NPD is a reproducible test for CF patients and thus may be a useful outcome measurement for assessment of the efficacy of new treatments.     

Effects of acute hypovolaemia by furosemide on tracheal transepithelial potential difference and mucus in dogs.

Furosemide is a potent diuretic that affects water transfer across the respiratory epithelium, which is closely related to the transepithelial potential difference (PD). Water is a critical factor that determines mucus transport; an important lung defence mechanism that removes particles and microorganisms from the respiratory system. The aim of the present study was to investigate the acute effects of furosemide and hypovolaemia on tracheal PD and mucus properties. A total of 36 male mixed-breed dogs were submitted to anaesthesia, mechanical ventilation and haemodynamic monitoring. They were randomly assigned to three groups consisting of: a control group, a furosemide (40 mg i.v.) + hypovolaemia group, and a furosemide (40 mg i.v.) + volume replacement group. Tracheal PD and mucus samples were collected at time 0, 1 and 2 h after intervention. Mucus properties were analysed by means of a magnetic microrheometer and in vitro mucociliary transportability on the frog palate. Compared to controls, furosemide decreased PD to intermediate values, and only significantly when associated with hypovolaemia (-13+/-5 and -8+/-2 mV, time 0 and 2 h, respectively). In addition to the direct effect of furosemide, these results indicate that hypovolaemia also affects ion transport in the tracheal membrane. Furosemide and hypovolemia have no acute effects on respiratory mucus properties.     

Amiloride-insensitive nasal potential difference varies with the menstrual cycle in cystic fibrosis

RATIONALE: There is no adequate explanation for gender-based differences in rates of mortality and of deterioration in pulmonary function in cystic fibrosis (CF) patients. One potential explanation is that gender hormones (sex steroids) may modulate the severity of CF lung disease, the principal cause of mortality in CF, by altering respiratory transepithelial ion transport. OBJECTIVE: To determine whether respiratory epithelial ion transport varied during the menstrual cycle of CF females. METHODS: The nasal transepithelial electrical potential difference (NPD) was determined as a measure of ion transport across human respiratory epithelium, coincident with measurements of endogenous serum hormone levels in the luteal and follicular phases of the menstrual cycle in CF females aged 16-22 years. RESULTS: The component of the NPD that is insensitive to the Na(+) transport blocker amiloride, but not the amiloride-sensitive component, changed in association with endogenous, menstrual cycle-induced changes in serum levels of progesterone and estrogen (P=0.02, n=7, paired t-test). Measurements using Cl(-) free perfusates suggested that the changes are not a result of Cl(-) conductance. CONCLUSIONS: Our results suggest that in CF respiratory epithelium amiloride-insensitive, but not amiloride-sensitive, ion transport is altered by female gender hormones in vivo. We speculate that amiloride-insensitive ion transport may contribute to the regulation of human airway surface fluid.     

Effects of heat-stable Escherichia coli enterotoxin on intestinal alkaline secretion and transepithelial potential difference in the rat intestines in vivo

The effects of the heat-stable enterotoxin of Escherichia coli (STa) on intestinal alkaline secretion and transepithelial electric potential difference (PD) were investigated in vivo in denervated segments of rat jejunum, ileum, and proximal colon. STa caused a significant increase in alkaline secretion in the jejunum but not in the ileum or colon. The jejunal effect of STa may be ascribed to a stimulation of bicarbonate secretion and/or an inhibition of Na+/H+ exchange. With regard to PD, STa caused a marked rise in colonic PD, whereas only a small response was found in the jejunum. No effect on PD was seen in the ileum. Hexamethonium (10 mg/kg intravenously) significantly diminished the effects of STa on PD, whereas only a small inhibition of the STa-induced alkaline secretion was observed. The effect of lidocaine on PD and alkaline secretion was found to be similar to that of hexamethonium. Atropine had no effect on any of the studied variables. These findings suggest that STa exerts, via nerves, a profound influence on the jejunal transport mechanisms responsible for the changes in PD, whereas the influence on alkaline secretion is to a large extent not mediated via enteric nerves. Thus, the extent of enteric nervous control of epithelial function differs for different transport functions. The findings also indicate that the bicarbonate ion is not the anion mainly responsible for the fluid secretion elicited by STa.     

A multicenter study of the effect of solution temperature on nasal potential difference measurements

BACKGROUND: Nasal potential difference (PD) measurement quantifies the abnormal sodium and chloride transport that is characteristic of cystic fibrosis (CF) and has gained acceptance as both a diagnostic tool and outcome measure for new CF therapies. Because small changes in nasal PD-measured chloride transport are often an important component in evaluating new CF therapies, techniques to maximize sensitivity and reproducibility are essential. STUDY OBJECTIVE: To determine if administration of warmed nasal PD solutions (37 degrees C), instead of room temperature solutions (22 degrees C), results in significant increase in nasal PD-measured transepithelial chloride transport. DESIGN: Multicenter, prospective, cross-over trial of repeated measurements of nasal PD at 22 degrees C and 37 degrees C. RESULTS: Thirty-two healthy volunteers completed the study (four centers, each with 8 subjects). For 22 degrees C vs 37 degrees C, baseline (+/- SD) nasal PD (- 19.3 +/- 6.9 millivolts [mV] vs - 18.8 +/- 7.7 mV, p = 0.76), amiloride-sensitive PD (Delta PD, 10.4 +/- 5.6 mV vs 11.0 +/- 6.1 mV, p = 0.60), and low chloride response (Delta PD, - 10.0 +/- 8.0 mV vs - 8.0 +/- 7.1 mV, p = 0.13) were not statistically significantly affected by warming of solutions. Warming solutions to 37 degrees C dramatically increased the chloride transport response to isoproterenol (Delta PD, - 6.9 +/- 6.4 mV vs - 13.3 +/- 8.8 mV, p < 0.01) and the combined total response to low chloride and isoproterenol (Delta PD, - 16.9 +/- 9.5 mV vs - 21.3 +/- 11.9 mV, p = 0.01). The average increases observed with warming in isoproterenol and combined total responses were - 6.4 mV (95% confidence interval [CI], - 8.5 to - 4.3) and - 4.4 mV (95% CI, - 7.6 to - 1.1), respectively. CONCLUSIONS: Performing nasal PD studies with solutions at 37 degrees C instead of 22 degrees C increases the observed total chloride response by approximately 25% and the isoproterenol-dependent chloride response by approximately 95%. The Cystic Fibrosis Foundation Therapeutics Development Network now recommends warming of solutions as a standard procedure for nasal PD protocols. Utilization of warmed solutions will standardize nasal PD techniques across centers and potentially increase the ability to identify therapies that result in small incremental improvements in CF transmembrane conductance regulator function.     

The effect of topical benzamil and amiloride on nasal potential difference in cystic fibrosis.

The electrochemical defect in the bronchial epithelium in cystic fibrosis (CF) consists of defective chloride secretion and excessive sodium reabsorption. The sodium channel blocker, amiloride, has been shown to reversibly correct the sodium reabsorption in CF subjects, but long term studies of amiloride have been disappointing due to its short duration of action. Benzamil, a benzyl substituted amiloride analogue, has a longer duration of action than amiloride in cultured human nasal epithelium. The results of the first randomized, placebo controlled, double blind, crossover study are reported here comparing the effects of benzamil and amiloride on nasal potential difference (nasal PD) in CF. Ten adults with CF attended on three occasions. At each visit baseline nasal PD was recorded, the drug (amiloride 1 x 10(-3) M, benzamil 1.7 x 10(-3) M, or 0.9% sodium chloride) was administered topically via a nasal spray, and nasal PD was measured at 15, 30 min, 1, 2, 4 and 8 h. Results were expressed as maximum change in nasal PD from baseline (PDmax), time for PDmax to return to 50% of baseline (t0.5), and the area under the curve (AUC). PDmax values for benzamil (20.6+/-0.9 mV) and amiloride (20.3+/-1.6 mV), were similar. The duration of effect was much longer for benzamil as measured as either AUC or t0.5 AUC values were 11.8+/-1.6 mV for benzamil, 2.8+/-0.4 mV for amiloride and 0.6+/-0.4 mV for placebo. The AUC value for benzamil was significantly greater than amiloride (95% confidence interval (CI) for the difference 5.3-12.7 mV, p<0.0001). t0.5 values were 4.3+/-0.7 h for benzamil and 0.6+/-0.1 h for amiloride (95% CI for the difference 2.0-5.3 h, p<0.001). It is concluded that benzamil has a similar maximal effect to amiloride but a more prolonged duration of action on nasal potential difference in cystic fibrosis. Benzamil may be a useful sodium channel blocker for the long-term treatment of the biochemical defect in the lungs of patients with cystic fibrosis.     

Potential difference across the normal and the abnormal gastric mucosa in man.

The mucosal potential difference in the body of the stomach was measured in 18 patients with gastric ulcers, five with gastritis, and three with pernicious anaemia. The results were compared with those of 12 normal volunteers. Significantly lower than normal levels were found in the groups of patients with gastric ulcers and gastritis. The patients with pernicious anaemia had even lower potential differences. In an additional 25 subjects, measurements were made in the duodenal bulb and at five sites in the stomach under direct vision at endoscopy. Biopsies were taken from each site for histology. Subjects with gastritis at the high lesser curve had a significantly lower potential difference at that site than those without gastritis. In the latter group, the potential difference at the high lesser curve was as low as in the antrum, and invariably lower than at the high greater curve.     

Effect of inhaled furosemide on metabisulfite- and methacholine-induced bronchoconstriction and nasal potential difference in asthmatic subjects

To evaluate the hypothesis that furosemide inhibits indirect bronchoconstrictor challenges by altering airway epithelial ion transport, we studied its effects on indirect bronchoconstriction induced by inhaled metabisulfite (MBS) and nasal potential difference (PD) in seven subjects with mild asthma. Its effect on direct bronchoconstriction by the inhaled muscarinic agonist methacholine (MC) was studied in six of these subjects. Each subject inhaled furosemide, 30 mg, in a randomized, double-blind, placebo-controlled fashion immediately before challenge with MBS (0.3 to 160 mg/ml in increasing doubling concentrations) and, in another study, MC (0.125 to 32 mg/ml) aerosols from a nebulizer attached to a dosimeter. PC20MBS and PC20MC, the concentration of each agent needed to lower FEV1 by 20%, were calculated by linear interpolation of the log dose-response curves. Furosemide had no effect on resting lung function, but it caused a significant threefold reduction in sensitivity to MBS (PC20MBS: GM +/- GSEM, 15.1 +/- 1.6 mg/ml after placebo and 40.7 +/- 1.7 mg/ml after furosemide; p less than 0.001) with a protective index of 64.8 +/- 10.7%. Furosemide caused no change in sensitivity to MC (PC20 MC:GM +/- GSEM, 2.37 +/- 1.61 mg/ml after placebo and 2.19 +/- 1.751 mg/ml after furosemide; NS). In a third study, furosemide, 30 mg, and placebo were inhaled through the nose in a randomized double-blind fashion immediately prior to inhalation of a PC20 concentration of MBS through the nose. Nasal PD was measured before and after placebo or furosemide, and again after MBS inhalation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Potential difference measurements in the lower airway of children with and without cystic fibrosis

Nasal potential difference measurements are valuable endpoint assays in clinical studies of novel treatments for cystic fibrosis (CF). Similar measurements made on the lower airway via the bronchoscope have been successful in adults, but have not been reported in children, the group most likely to benefit from such therapies. Here we report the design and validation of a small, single-lumen catheter technique allowing baseline potential difference and chloride secretion to be assessed in the distal airways of children as young as 1 year of age. Tracheal baseline values were significantly higher in children with CF than those without, although this was not the case more distally. In airways between the third and seventh generation, perfusion with a zero chloride solution containing isoprenaline led to a significant change in potential difference in children without CF, whereas no change was seen in those with CF. This measure provided a reliable distinguishing test between the two disease groups. We confirm that invasive bronchoscopic techniques can be performed safely and reliably in small children. Potential difference measurements could form a useful functional endpoint assay for future studies of either the CFTR gene or protein-based therapies in future trials in the pediatric age group.     

Sodium channel blockers and uridine triphosphate: effects on nasal potential difference in cystic fibrosis mice.

Sodium channel inhibitors block the enhanced Na+ reabsorption in cystic fibrosis (CF). Extracellular nucleotides facilitate Cl- secretion via Ca2+ gated Cl- channels. A combination of these effects may produce less viscid secretions in CF which are easier to expectorate. This study examined the effects of combining sodium channel blockers with uridine triphosphate (UTP) on nasal membrane potential difference (PD) in CF insertional null mutant mice (cftr(tm1HGU)), deltaF508 homozygous mice (cftr(tm1Cam)) and matched control animals. Median basal PD in the insertional CF mice and deltaF508 CF mice were -28 and -34 mV respectively. These values were significantly different to the control animals (-20 mV). Amiloride and loperamide reduced the PD in cftr(tm1HGU) CF mice (deltaPD 13 mV & 15 mV respectively) suggesting Na+ blockade. The subsequent addition of UTP in a chloride-free vehicle increased the PD (deltaPD -8- -12.5 mV). DeltaF508 mice showed significantly greater responses compared with CF insertional null mutant mice (p<0.05). The action of UTP was brief and not prolonged by the addition alpha-beta-methylene-adenosine 5' diphosphate. Suramin, a competitive antagonist of P2 purinoceptors blocked the action of UTP. In conclusion, this study demonstrated dose dependant nasal membrane potential changes in differences mice with uridine triphosphate in the presence of sodium channel blockers suggestive of chloride secretion. More stable analogues of uridine triphosphate in combination with long acting sodium channel blockers such as loperamide may have therapeutic potential in cystic fibrosis.     

Standardized procedure for measurement of nasal potential difference: an outcome measure in multicenter cystic fibrosis clinical trials

Patients with cystic fibrosis (CF) can be discriminated from healthy subjects by measurement of the nasal potential difference, which has become a useful outcome measure for therapies directed toward correcting defective electrolyte transport in CF. A standard operating procedure was developed by a CF Foundation clinical trials network, to be followed by all sites performing collaborative studies. Key variables in the measurement included type of voltmeter, exploring probe, reference electrodes, and solutions used to assess both sodium transport and chloride conductance. Eight sites submitted data on 3-8 normal and 4-5 CF subjects. Baseline voltage, an index of sodium transport, was -18.2 +/- 8.3 mV (mean +/- SD) for normals, and -45.3 +/- 11.4 mV for CF patients. There was no CFTR-mediated chloride secretion in CF subjects, as evidenced by the lack of response to perfusion with zero chloride + beta agonist solutions (+3.2 +/- 3.5 mV) vs. that in normals (-23.7 +/- 10.2 mV). The standardized nasal potential difference measurement minimizes variability between operators and study sites. Valid and consistent results can be attained with trained operators and attention to technical details. These data demonstrate the procedure to be sufficient for multicenter studies in the CF Foundation network.